Building assemblies are known which have a foldable capability so that they may be erected where desired and, when necessary, folded up to a rather compact form for storage and/or transportation. These building structures are based upon column-like elements or rods which are used as basic construction units which function as stays. The links are interconnected with pivot joints, slip joints or other forms of movable interconnects, so that a collapsible, articulated structure is formed. A fabric covering is usually associated with the network of rods. An example of such a collapsible structure is shown in U.S. Pat. No. 3,185,164 which shows a structure including a plurality of rods joined by couplings into groups of three which are inter-related to form a generally hexagonal structural system. Another example of such a collapsible structure is shown in U.S. Pat. No. 3,710,806. Structures which utilize elements intended to maintain the rigidity of the structure are also known, as exemplified in U.S. Pat. No. 3,063,521.
The prior art is also generally cognizant of the use of collapsible frame structures for supporting tents or other outdoor shelters. Examples of collapsible frames for use in supporting such tents or outdoor structures are shown in U.S. Pat. No. 563,376; U.S. Pat. No. 927,738; U.S. Pat. No. 1,773,847; and U.S. Pat. No. 2,781,766. Such structures have varied widely in their ease of erection and storage, and are of varying structural strength.
Structures which are in the form of a dome or sphere are of interest because this shape achieves greater strength than other geometric shapes for the materials used. A dome structure also provides a great deal of interior space with a minimal amount of base area and building materials. However, spherical structures involve complex construction and difficult geometric relationships between the structural members. The complexity increases further when it is desired that the dome structure have a collapsible capability.
Attempts have been made to convert a plurality of flat planes into a spherical surface. Buckminster Fuller defined the spherical icosahedron (i.e., a polygon having 20 faces) by projecting a flat triangular grid onto the surface of a sphere. He utilized a 60 degree coordinate system, based on a triangular shape, which is very structurally stable. Fuller's icosahedron, as disclosed by U.S. Pat. No. 2,682,235, is known as a geodesic dome. However, Fuller's geodesic dome does not have a collapsible capability; rather, it is intended to be constructed by the user at the site of usage. For these reasons, the geodesic dome design is not always a practical structure.
In U.S. Pat. No. 3,968,808, issued July 13, 1976, Theodore Zeigler utilized Fuller's icosahedron in the form of a folding, self-locking structure. No new geometry was introduced. The patent discloses a self-supporting domed shelter constructed from a series of intermeshing pentagonal or hexagonal sections, each section being composed of crossed pairs of pivotally connected struts. The generally semi-spherical framework is made of elongate struts and hub means which are movable between a collapsed, bundled condition (in which the struts are closely bundled and in a generally parallel relationship) and an expanded condition of three-dimensional form. The structural framework as disclosed in this patent is self-supporting by virtue of self-locking action which results from the asymmetrical disposition of certain struts. The framework has zones of sliding connections between crossed struts, as for example at 110 in FIG. 1, which allows the structure to be collapsed.
In Zeigler's U.S. Pat. No. 4,026,313, each icosahedron face has alternate zones 18 and 20 of sliding and pivoted connections as shown in FIG. 1 of that patent. FIGS. 10-12A illustrate rectangular modules. U.S. Pat. Nos. 4,290,244 and 4,437,275 are divisions of U.S. Pat. No. 4,026,313 and are directed to structural modules.
As explained above, Buckminster Fuller converted a flat plane into a spherical surface or compound plane of several axes to form an icosahedron. Theodore Zeigler's later work, as shown for example in U.S. Pat. No. 4,689,932, converted a flat plane into a spherical surface, but in a different manner. Zeigler defined the octahedron shape, which allowed the ability to build long narrow structures or tall wide structures. An octahedron is a solid bounded by eight plane faces. With the octahedron based design, the struts which define the structural modules may be of equal length.
The octahedron design developed by Zeigler also introduced the 90-45 degree coordinate system. This design permits "stretchability" on three axes because each of the modules has the same edge lengths. That is, the controlled addition of modules permits the basic octahedron to be dimensionally increased in three mutually orthogonal directions: in height, in width and in length.
Zeigler's U.S. Pat. No. 4,689,932 employed the above octahedron concept to form a dome structure composed of square modules. This patent is incorporated by reference herein. The patent disclosed two types of modules: a "flat" module and a "transition" or cylindrical module. The circumscribing sides of all the modules are formed by crossed, pivotally connected struts.
With this design, the resulting building has a generally spherical shape which is substantially horizontal at the top of the structure and substantially vertical near the bottom of the structure, there being a curved portion therebetween formed by the transition modules. With this design, the corner portions of the building are left open if, for example, passageways are desired, as shown in FIGS. 1-3 of U.S. Pat. No. 4,689,932. As the size of the structure is increased, these open corner sections become progressively larger. The prior art does not address the problem of completely closing off the corner portions of the octahedron structures.
In regard to prior building designs, including the geodesic dome design and conventional structures such as frame tents, there are several general problems. If the structure is of the expandable/collapsible type, the structures are often difficult to erect, and require several workers, a significant amount of time, and special tools and equipment. The structures are also often complex in construction, having several different detachable parts and being relatively heavy and bulky in size. The non-uniformity of the size of the structural members also contributes to the overall complexity and cost of such structures. Many conventional structures, such as frame tents having a flat roof, are limited in their aesthetic appeal. As a result, the number of applications for which these structures are appropriate is limited.
The present invention addresses these and other problems associated with known collapsible support structures.